1. Field of the Invention
This invention relates to electrophotographic copiers, and more particularly to an electrophotographic copier capable of automatically making two-sided copies.
2. Description of the Prior Art
It is well known that the almost universal acceptance of electrophotographic copiers has served to greatly facilitate general access to information. At the same time, however, copier usage has not gone totally without creating some ancillary problems such as the burden both on the amount of paper consumed and the space required to store the resultant copies. The paper problem stems in part from the fact that while many documents have printing on both sides of a sheet, many prior art electrophotographic copiers were designed for making copies on only one side of a receiver sheet (hereinafter referred to as one-sided copying).
As is readily apparent, the formation of a copy on both sides of receiver sheets would save both on the amount of paper used as well as the space required for storage. Therefore, several recently introduced plain-paper electrophotographic copiers have provided for simple manual two-sided copying (copying on both sides of a receiver sheet). In order to accomplish this end, receiver sheets on which a copy has been made of the first side of a document (first-side copy) are manually transferred from the exit hopper back to the sheet supply. The side of each sheet on which the copy was made is oriented oppositely to its orientation during initial (first-side copy) feeding. The sheets may then be fed to have the copy of the second side of the document (second-side copy) made thereon. While this method of two-sided copying does not require additional machine structure, it does require an additional manual operational step with some coincident sophistication in operation training to insure proper image registration for copying in the two-sided mode of operation.
An attempt to provide automatic two-sided copying in an electrophotographic copier is shown in U.S. Pat. No. 3,645,615 in the name of Spear, issued Feb. 29, 1972. The first-side copy is made on sheets fed from a main paper supply, the sheets being delivered (after the first-side copy image is fused thereto) to a second paper supply. The second-side copy is then made by feeding the first-side copy sheets from the second paper supply, the sheets being subsequently delivered to the exit hopper after the second-side copy is made. As can be seen in FIGS. 1 and 2 of this patent, two paper feeders, two "entrance" paths and two "exit" paths are required.